1. Field Of The Invention
This invention relates to the cylinders of an internal combustion engine and has particular reference to a process for the construction of cylinders having liners disposed within the bores thereof.
2. Related Art Statement
The cylinder bore walls of internal combustion engines must be made of a material which will provide resistance to the abrasive action of the combustion seal rings of a piston. In traditional cast iron engine blocks, cast iron alone will provide sufficient wear resistance for the life of the engine. However, in applications where a lighter weight engine block material is used, such as aluminum, liners must be inserted into the cylinder bores to provide the required wear resistance.
In the past, there have been various approaches to the "shrink in place" or "press-in" cylinder bore liners. Such approaches include the steps of heating a partially machined cylinder block to 400.degree.-450.degree. F. to expand the cylinder bores. Precision machined liners are then inserted therewithin. As the block cools, the aluminum contracts, and the liners become secured in place.
Other related methods include shrinking the liners by cooling them in a substance such as liquid nitrogen and inserting them into an ambient temperature engine block casting whose bores have been machined to a diameter slightly smaller than the ambient temperature outside diameter of the liner to create an interference fit. Another method, less often used, is simply to press liners, whose outside diameters are slightly larger than the cylinder bores, into engine block castings at ambient temperature.
These processes without modification tend to produce a deficiency in the finished engine which is referred to as liner migration: radial and axial movement of the liner during engine operation.
Another approach commonly used for liner insertion, referred to as cast-in liners, makes the liner an integral part of the engine block casting during the casting process. This can be accomplished using many traditional metal casting processes including die casting, semi-permanent mold and low pressure casting.
In many conventional cast-in liner aluminum block processes, notably those having metal molds, liners are typically preheated with a suitable device (such as a furnace, radiant heater, induction heater, etc.) outside the mold, before mold assembly. Such liners are then installed on mandrels within the mold.
Processes which utilize an all sand core mold render the insertion of liners during mold assembly virtually impossible. This is because the mold assembly requires complex juxtaposition of mating cores, which takes time during which a heated liner would otherwise cool. Earlier experience has led to an interest in determining whether methods might be available to heat the cylinder bore liners within the assembled mold package.
In the past, cast-in liners have been viewed as not being feasible in high volume production using sand casting processes because of the difficulty with heating the liners and inadequate control of liner location. Accordingly, it would be beneficial to have available cast-in liners which would eliminate liner migration and to reduce engine plant facility investment.
Relevant to the goal of economical manufacture of internal combustion engines are the requirements of economy in machining, simplified castings, and ease of assembly. The present invention addresses these requirements in a manner set forth below.